The present invention relates generally to an electrical connector and, more particularly, to a filter electrical connector for reducing electro-magnetic interference.
A problem which is frequently encountered by users of electronic equipment is that of electro-magnetic interference (EMI). For example, complex solid state PBX systems utilized by the telephone industry are susceptible to interference from a number of noise generating sources. In addition, the high frequency switching circuits of the systems can also be a source of noise. Such interference may be reduced to some degree by enclosing the electronic equipment in a tight metal cover to provide an EMI tight structure. However, the problem still exists of economically filtering the hundreds of signal leads entering and leaving the PBX cabinet.
The ideal location for filter units is inside the connector for the signal leads. Filter connectors are well known in the art. In one form, each electrical contact in the connector is provided with its individual filter assembly, including a plurality of small ferrite annular elements and a fragile ceramic tube which are assembled together in proper fashion to form the filter.
In another form of prior art filter construction, the inductance is provided by a ferrite disc having a plurality of apertures for receiving connector contacts, thereby minimizing the number of parts required. Also, a conductive disc having a plurality of apertures receiving the terminals has been employed as a part of a capacitor feature of the filter. However, an individual dielectric tube for each capacitor is required.
The following U.S. patents disclose filter connectors of the general type discussed hereinabove: U.S. Pat. Nos. 3,002,162; 3,447,104; 3,535,676; 3,573,677; 3,721,869; and 3,854,107.
It will be appreciated that the filtering techniques employed in the connectors described hereinabove and in the aforementioned patents are not practical for connectors having a large number of contacts, such as telephone connectors, because a large number of parts are required to provide the filtering capacity, which results in costly construction in terms of manufacturing and assembly. A typical connector utilized in the telephone industry is disclosed in U.S. Pat. No. 3,002,176 to Yopp and incorporates 50 contacts. Furthermore, such filtering arrangements cannot be readily incorporated into connectors already installed in the field since the filter elements must be mounted around the contacts in the connectors.
An alternative form of filter connector is disclosed in U.S. Pat. No. 3,538,464 to Walsh. The Walsh patent discloses a filter connector utilizing a multi-layer monolithic ceramic capacitor. The contacts in the connector extend through apertures in the capacitor. Alternate line electrode plates in the capacitor extend into the wall of each aperture and are joined by a conductive layer on the wall which is in turn connected to the contact in the aperture. Capacitor ground plates are embedded in the dielectric substrate of the capacitor between the live electorde plates and extend to the outer periphery of the substrate where they are electrically connected to the housing of the connector. While such a structure minimizes the number of parts required to provide filtering capacity in a connector, it has the disadvantage that, like the other filter connectors discussed above, the capacitor assembly is a feed through arrangement. That is, the contacts must be mounted through the capacitor units.
The prior art feed through filter arrangements are not practical for incorporation into connectors already installed in the field. Furthermore, feed through filter arrangements could be incorporated into standard connectors, such as those utilized in the telephone industry, only by completely redesigning the connector and retooling, which would be very costly.
The purpose of the present invention is to provide low cost and convenient filtering capacity for already installed telephone systems or the like which will not require replacement or modification of the connector presently utilized in the systems. Another object of the invention is to provide filters in standard connectors without requiring reconstruction or redesign of the connectors.